The invention relates to a control device for semiconductor switches of an inverter and to a method for actuating an inverter, in particular for operating an inverter in a rapid discharge mode.
Electric and hybrid vehicles often have power electronic circuit components in the drive system between the fraction battery and the electrical machine, which components are usually constructed as voltage intermediate circuit converters. In this case, a DC voltage intermediate circuit is used as the coupling element between the traction battery and an inverter which can be actuated in order to transmit electrical power from the DC voltage intermediate circuit to the electrical machine.
Inverters may be, for example, in the form of a full-bridge circuit with a number of bridge arms with two semiconductor switches each. In this case, those semiconductor switches of the bridge arms which are connected to a first output connection of the DC voltage intermediate circuit may each be referred to as high-side switches and those semiconductor switches of the bridge arms which are connected to the second output connection of the DC voltage intermediate circuit may each be referred to as low-side switches. In this case, IGBT modules (bipolar transistors with an insulated gate electrode) with a diode reverse-connected in parallel or MOSFETs (metal oxide field effect transistors) can be used as semiconductor switches, for example.
Control systems which generate switching signals for the semiconductor switches are used to actuate the inverter. In the event of a fault, different demands are imposed on the control systems for reasons of safety. For example, it may be necessary to safely short-circuit the motor windings of the electrical machine in the event of a fault. This may be effected by closing all high-side switches and opening all low-side switches (or vice versa), which is also referred to as an “active short circuit”.
In addition, it is necessary, in the event of a fault, to rapidly and reliably discharge the DC voltage intermediate circuit, in particular also if supply voltages in the control system fail. This may be effected by means of a rapid discharge. Such a rapid discharge is normatively required within a maximum rapid discharge time of five seconds in order to be able to ensure the electrical operational reliability of the vehicle.
The document US 2005/0231171 A1 discloses an electrical drive system having an electric motor, a pulse-controlled inverter and an intermediate circuit capacitor. The intermediate circuit capacitor can be discharged in a controlled manner via a corresponding switch mode of the pulse-controlled inverter.